This invention relates to a vibration isolator assembly that generically refers to a device that absorbs vibrations and dampens relative movement between two structures, such as an isolator mount, bushing assembly, cradle mount assembly, etc.
A typical vibration isolator includes an external housing and an internal mounting shaft joined by an isolator such as a molded elastomer (e.g., rubber). The elastomer provides isolation between the housing and the mounting shaft. Typically, the elastomer is molded to the housing shaft in a high-temperature molding operation. This provides a desirable bond between the elastomer and the housing, as well as between the elastomer and the mounting shaft. After the molding operation, the elastomer experiences shrinkage as the part cools. Depending on the design, an undesirable effect of this shrinkage is to impart tensile stress to the elastomer. In such cases, fatigue performance of the vibration isolator assembly is generally improved by relieving the stress. One common way of relieving the stress is to pass the external housing through a funnel or reduced diameter opening to permanently reduce the diameter of the assembly. Such an arrangement is shown and described in the prior art representation of FIGS. 11–13 of U.S. Pat. No. 6,094,818, and is also well known to one skilled in the art.
Also, due to general poor fatigue performance of an elastomer under tensile loading, further enhancements to fatigue life may be realized by going beyond the simple relief of imparted tensile stresses and imparting compressive stress to the elastomer. Unfortunately, conventional methods for reducing the outer diameter of the isolator are limited in their effectiveness when there is a desire to impart compressive stress to the elastomer. This is due, for example, to negative effects on the bonding between the isolator and housing materials, i.e., the adhesive layer bonding between the isolator and housing, and isolator and the mounting shaft. There are also limits on the extent of deformation that the housing material can undergo.
It will also be appreciated that a substantial amount of time and money are required to design, redesign, tool, and retool a product. The development cycle requires significant design and engineering time to be sure that the final product meets the final product specifications. If the specifications are altered during the development process, a need exists to remove, modify, and reinstall the assembly in a short time frame. With regard to producing manufactured mounting and vibration isolators for power trains, i.e., engines/transmissions in various consumer and commercial vehicles, as well as a development tool for engineering purposes that allows optimization and tuning of a power train mounting system for improved isolation and performance, a need exists to address tuning and durability issues. If such issues surface late in a program cycle, it is necessary to implement changes without a major redesign or a long retooling time, even though the basic characteristics of the isolator are being modified.
Thus a need exists to enhance the durability and tuning ability of a vibration isolator assembly. Means to relieve residual tensile stress, as well as vary the level of precompression of the elastomer portion, are desired. A need also exists to vary the travel limits of the elastomer portion. Lastly, there is a need to overcome these problems without major reworking of prototype or production tooling.